I found this recipe on liquor.com.

cognac, creme de cacao, cream⁣
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I have so much to say about this drink! Recently, I did drinks on two themes – 1980s cocktails, and fake martinis. There was a lot of heavy cream used in those drinks, and for the most part, they were heavy and sweet and terrible. This is not one of those!⁣
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Brandy Alexander is a classic for a reason. The balance of the booze bite, sweetness, and cream is just right. I was kind of blown away by the first sip, and I thought, “this is what to serve people who don’t like egg nog!”. I know egg nog is polarizing…offer this AND egg nog at a Christmas party and everyone will be happy. ⁣
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Oh! I should mention that the recipe actually calls for dark creme de cacao, and I used white creme de cacao. I’m not sure how much difference that makes, other than the color.⁣
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Now to the history. Brandy Alexander is actually a riff on an Alexander, which is the same drink with gin instead of cognac. The exact history on the drink is lost and/or disputed, but the recipe is believed to be about 100 years old.⁣